SU900946A1 - Slag-forming powdered mixture - Google Patents

Description

(54) SLAG FORMULA POWDER

I

The invention relates to ferrous metallurgy, in particular, to protective mixtures used in steel casting.

Known slag-forming mixture 11 to protect the metal during the casting process, containing, wt.%:

Portland cement

basis 5-20

Calcium fluoride

20-40

Fireclay powder 2-15

Soda 2-15

Borax

Distending agent

0.01-0.5

(vermiculite, mica)

The disadvantages of the mixture are the complexity and complexity of the conspiracy.

The known chisak-forming mixture 2J for casting, containing, wt.%:

Mica10-30

Cryolit2-20

Graphite2-10

Fluorspar10-25

Portland cementEarly MIXTURE

The disadvantage of the mixture is the use of cryolite, which worsens sanitary conditions in the workplace.

Closest to the offer is a slag-forming mixture of 3 dl. casting steel, containing, wt.%:

Nepheline 10-40

Carboniferous

substance2-15

Silicate clumps5-30

ten

Fluorspar2-10

According to the balance do100

Cement

The disadvantages of the mixture are the difficulty of preparation, the limited storage time, and not because of the significant content of the hygroscopic silicate block. In addition, when using conventional carbonaceous substances — graphite (amorphous or crystalline) or coke, a reducing atmosphere is not created above the slag. The metal is oxidized through a layer of protective slag, the surface layer is contaminated with alumina inclusions, as a result of which the quality of uninterrupted castings deteriorates and the yield of the metal decreases. The purpose of the invention is to reduce the content of alumina non-metallic inclusions in the surface layer of an ingot and to increase the yield of a suitable metal. The goal is achieved by the fact that a powdered mixture containing carbon-containing nepheline material, fluoride rod Portland cement, silicate lump, contains coal powder as a carbonaceous material in the following ratio, wt.%: Nepheline 20-30 Fluor spar 20-25 Silicate lump 2-4 Stone coal U-20 Portland Cement28-41 On the metal mirror in the mold, the slag-forming mixtures form a three-layer coating consisting of liquid slag, a sintered and a central layer. The melting point of the mixture is 1120-1180 ° C, the viscosity of the slag at a casting temperature of about 1 P. Nefelin is the main source of silicon oxides, aluminum and alkali metals. Moreover, these oxides are in a chemically bound state, which accelerates their melting. With a C () holding of nepheline less than 20%, the melting temperature of the mixture is unacceptable, and with a nepheline content of more than 30%, an undesirable sprouting of curtains on the walls of the crystallizer is observed. Fluke pshat is smooth. The upper limit of 25% fluorspar is limited by the possibility of formation of excessively liquid slag, which is associated with its high costs and deterioration of the quality of the ingot. The lower limit of 20% fluorspar content is limited by the possibility of increasing the viscosity of the slag, which degrades the surface quality of the ingot in the event of poor slag performance. A silicate block accelerates the fusion of all components of the mixture. When its content is less than 2%, the effect of accelerating the fusion of the mixture is negligible. An increase in the content of silicate lump more than 4% is impractical due to the increased hygroscopicity of the mixture. Coal is a rock of plant origin. Its calorific value is 7-8.6 thousand kcal. (on combustible mass). It is introduced into the mixture to create a metal and slag above the mirror of the reducing atmosphere due to incomplete combustion of carbon and the release of a large amount of volatile substances. In addition, during the oxidation of coal by oxygen of the air, heat is generated, which partially compensates for the heat of the metal used to melt the mixture. You can use the waste of coal, for example, in the form of dust. Coal or waste with a volatile matter yield of more than 20% is well sintered. The sintered layer serves as a regulator of the rate of melting of the mixture and its specific consumption. When the content of coal is less than 10%, the necessary heat-insulating properties of the slag coating are not provided and insufficient quantity of heat is emitted, which is especially important when casting at low speeds. When the content of coal or its waste in an amount of more than 20%, there is a danger of carburizing the metal, since the thickness of the liquid slag and the sintered layer are unacceptably reduced. When the content in the coal or its waste of volatile substances less than 20% above the slag mirror does not create a reliable protective atmosphere. In addition, the sintering of the coal powder or its waste is deteriorated, which leads to a sharp increase in the mixture consumption and deterioration of the surface quality of continuously cast billets. Spider-like cracks are observed on their surface. The formation of cracks on the surface of continuous castings is also observed with increasing sulfur in coal or its waste by more than 4%. The mixture is prepared by thoroughly mixing the pre-milled components and used to feed the crystallizer during continuous casting of steel. The mixture is easy to manufacture, uniformly mixed, has a homogeneous composition. In addition, it is slightly hygroscopic and does not clot during storage. During steel casting, the specific consumption of the mixture is within 1 kg / ton. The mixture forms a slag that holds well on the metal mirror. The oxygen content above the slag surface in the crystallizer does not exceed 5%. The content of non-metallic inclusions in continuously cast billets is 10-15% less than when casting them using a known mixture. Billets, cast using the proposed mixture, have virtually no surface defects. Example. Mixtures 1-3 are prepared by mixing dosed quantities of pre-milled initial components of nepheline, hydrofluoric ishat, silicate clumps, coal with a volatile content of more than 20% and sulfur less than 4% and portland cement. Portland cement is introduced into the mixture in powder form.

The compositions of mixtures are given in Table.

In a similar way, mixture (4) is prepared using amorphous graphite as a carbon-containing substance.

Compared with the known mixture (4), the proposed mixtures (1-3) are more technological in preparation, since the mixtures are better mixed and retain their homogeneous composition during storage. In addition, they are less hygroscopic and last longer from preparation to use.

The mixtures are tested during casting of carbon and low-alloyed steel and in a continuous casting installation to protect the metal surface in the mold during the casting of a slab with a section of 250x1600 mm.

In the process of casting steel under the well-known mixture 4 observe its work. The requirement is to periodically remove the slagged skull in the corners of the mold. Spider-like cracks are observed on the surface of the slab. When casting steel slabs with a residual aluminum content of 0.02-0.06%, the contamination of the metal with alumina inclusions in the surface zone, in the region of the fold depressions, is in the range of 0.06-0.07%

bulk. Along the valleys of the folds, transverse cracks are observed; on the surface of the slabs, spider-like treaoshes are observed. The oxygen content in the crystallizer above the slag coating is within 15%. Sheet yield is 95%.

When casting steel under mixtures 1-3 pelletizing is not observed. There is no slag formed in the mold. There are no transverse and arachnoid cracks on the surface of the slab. When casting steel slabs with a content of residual aluminum of 0.02-0.06%. The contamination of the alumina metal with inclusions in the surface areas, in the area of the fold depressions, is within 0.04-0.05% by volume. The oxygen content above the slag layer in the crystallizer does not exceed 5%. The yield of sheets from slabs cast under mixtures 1-3 is 96.6%.

Thus, the use of the inventive mixture makes it possible to reduce the content of gly; non-metallic non-metallic inclusions in the surface layer of continuous-cast billets and increase the yield of the metal by an average of 1.5%.

Nepheline Coal

thirty

25

25

Claims (1)

boo, fluorspar, Portland cement, characterized in that, in order to reduce the content in the surface layer of the ingot of alumina non-metallic incl. values and increase the yield of metal, as a carbon-containing substance, it contains coal powder in the following ratio of components, wt.%: Nepheline 20-30 Fluorspar 20-25 VNIIIPI Order 12257/7 Circulation KL.